Candace X. Moore

Co-secretion of amylin and insulin from cultured islet beta-cells: modulation by nutrient secretagogues, islet hormones and hypoglycemic agents.

Amylin is a pancreatic islet beta-cell peptide hormone which modulates carbohydrate metabolism in skeletal muscle and liver, and could contribute to impaired insulin sensitivity in Type II diabetes. Here we report the first description of amylin secretion from isolated beta-cells. We measured amylin secretion from HIT T15 beta-cells exposed to glucose, arginine, glucagon, somatostatin, tolbutamide, glyburide, or metformin. With the exception of glucagon at concentrations above 1 microM, all compounds induced parallel, dose-dependent changes in secretion of amylin and insulin. We conclude that: 1) insulin and amylin are co-secreted from islet beta-cells; (2) nutrient secretagogues and peptide modulators exert direct effects on beta-cells to alter amylin and insulin secretion; (3) most modulators of islet beta-cell secretion alter amylin and insulin in parallel, but differential secretion can occur; and (4) HIT cell line is a useful model in which to study amylin metabolism.

Preclinical pharmacology of pramlintide in the rat: Comparisons with human and rat amylin

The pancreatic β‐cell hormone, amylin, is absent or reduced in individuals with type I diabetes mellitus and in many insulin‐treated patients with type II diabetes. Amylin replacement therapy may be beneficial in these individuals, but the pharmaceutically inconvenient physicochemical properties of native human amylin led to the development instead of the amylin agonist, [Pro25,28,29]human amylin, or pramlintide (formerly designated AC137). Here we compare for rat amylin, human amylin and pramlintide, receptor binding and biological actions in rats in vivo and in rat soleus muscle. In the rat, the spectrum of actions and pharmacokinetic and pharmacodynamic properties of pramlintide are either very similar to, or indistinguishable from, those of rat or human amylin.

Molecular cloning of two receptors from rat brain with high affinity for salmon calcitonin

Two receptors with high affinity for salmon calcitonin were cloned from the nucleus accumbens region of rat brain. The deduced 479 amino acid sequence of cDNA clone L2175‐D20 (designated Cla receptor) is 78% and 66% identical with those reported for human and porcine calcitonin receptors, respectively. Clone U3237‐A2 codes for a receptor (designated Clb) that is identical to Cla except for a 37 amino acid insert in the second extracellular domain. COS‐7 cells transfected with either transcript bound [125I]salmon calcitonin with high affinity (K d = 8 pM for Cla; K d = 48 pM for Clb) and responded to salmon calcitonin with increases in cAMP. Tissue distribution studies revealed Cla transcript in rat brain, skeletal muscle, kidney and lung, whereas Clb was predominantly found in brain.

SPECIAL REPORT Regulation of muscle glycogen metabolism by CGRP and amylin: CGRP receptors not involved

The aim of the present study was to determine whether amylin and calcitonin gene‐related peptide (CGRP) act through shared or distinct receptors to inhibit insulin‐stimulated incorporation of [14C]‐glucose into glycogen. Rat amylin was 3 fold more potent than either rat αCGRP or rat βCGRP at reducing glycogen synthesis from [14C]‐glucose in insulin‐treated rat soleus muscle. This action was blocked by peptide antagonists, with the rank order of potency being AC187> salmon calcitonin 8–32 (sCT8.32) > h‐αCGRP8–37 for antagonism of either amylin or CGRP. The antagonist potency order correlated with affinity for amylin receptors measured in rat nucleus accumbens but not CGRP receptors measured in rat L6 muscle cells. Inhibition of glucose incorporation into glycogen by amylin and CGRP appears to be mediated by shared receptors that have the pharmacological characteristics of amylin receptors, and are distinct from previously described CGRP receptors.

Comparison of the in vitro and in vivo pharmacology of adrenomedullin, calcitonin gene-related peptide and amylin in rats

Adrenomedullin has been reported to be structurally similar to a group of peptides that includes amylin, calcitonin and calcitonin gene-related peptide (CGRP). Human and rat adrenomedullin displaced [125I]CGRP from membranes of SK-N-MC cells (CGRP receptors) with affinities intermediate between those of rat amylin and rat CGRP alpha (Ki values 0.12 +/- 0.06, 0.017 +/- 0.007, 3.83 +/- 1.14 and 0.007 +/- 0.001 nM, respectively). In contrast Ki values for displacement of [125I]rat amylin from accumbens membranes (amylin receptors), and [125I]salmon calcitonin from T47D cells (calcitonin receptors) were lower than with rat amylin or rat CGRP alpha in these preparations (51 +/- 5, 34 +/- 2, 0.024 +/- 0.002, 0.31 +/- 0.07 nM, respectively, at amylin receptors; 33 +/- 5, 69 +/- 29, 2.7 +/- 1.5 and 13 +/- 3 nM, respectively, at calcitonin receptors). In anesthetized rats, the hypotensive potency of adrenomedullin was between that of amylin and CGRP alpha. In contrast, for amylin or calcitonin agonist actions (inhibition of [14C]glycogen formation in soleus muscle, hyperlactemia, hypocalcemia and inhibition of gastric emptying), human adrenomedullin was without measurable effect. Thus, in its binding behaviour and in its biological actions, adrenomedullin appeared to behave as a potent CGRP agonist, but as a poor amylin or calcitonin agonist.